What Causes Frequent Outbreaks Of Itchy Hives All Over The Body?

Hi, Every time I visit Fiji Islands I breakout into hives all over my body which is very itchy and feel sick. The only thing I can think of is that they use Mortein bug/ mosquito spray. Because I have families in Fiji, I will be visiting the Island but I am always scared of the side or allergy effects on meEvery visit I get hives and use anti-histamines which never works for me until I come back home/Canada and end up in emergency when I am prescribed high dosage like Benadryl ++. . Please can you suggest what I should take with me during my next visit. Thank you, Premila